Lots of things could've happened as has already been mentioned. A rematch would probably have taken place, and much as I admire Rudkin, it might've been a lot to expect him to repel Harada - yet to eat his way up to featherweight - a second time, though far from impossible, especially in the UK. The fight was sandwiched between both Harada-Jofre fights too, so that's another potential can of worms right there. I hope Al Jr weighs in on this, 'cos I think a fight with Jofre was in the works until Rudkin got slightly scabbed against McGowan first time around, which led in turn to him being frozen out of the world scene and having to go out to Barcelona in '67 only to get cheated against Ben Ali. Incidentally, Ben Ali himself was high up in the rankings himself in '66, as was Pimentel, so if we imagine a scenario whereby Alan somehow either beats or bypasses Harada and Jofre, we might've seen those two jostling with Medel, Caraballo and McGowan for a crack (with Medel probably at the front of the queue having sunk Pimentel, Corona, Wee Walter and Saito).
Rudkin vs Medel is an interesting one and I have a slight suspicion that Flea might not be too far from the truth with his summary, although Alan's classical stand-up, centre of the ring style would make for a testing clash with Medel's two-fisted power, slickness and trickery. I'd be more confident if I knew for certain that he (Rudkin) would keep the exchanges at ring-centre, where he was at his best, rather than being drawn to the ropes. Big no-no against Medel. Great fight though, hopefully with Rudkin's jaw, work rate, discipline and range control being enough to see him through. Wouldn't put money on it though.
I'd back Rudkin to circumnavigate Caraballo and Pimentel, though not without some difficulty. Pinto, Saito etc he should also turn over and if we're honest, he really beat Ben Ali despite not getting the decision.
Rose was ranked in '66 too iirc, though if any fictional timeline played out like the actual one, it would be a couple of years circa '68 before he, Sakurai and Castillo entered the mix soon to be followed by Olivares. How's that for fairness?
As mentioned earlier, Rudkin suffered a bit from not getting the fights between '66 and '68, though I suppose it's possible that tackling Harada (again), Jofre, Medel, Pimentel, McGowan and Caraballo in such a short space of time might have burnt him out a bit quicker before Rose and whatnot came along, with his overall legacy potentially very different, for better or for worse.